Abalone, in the natural state, are fast being depleted by predators, ocean pollution and commercial harvesting, to the point that there is no longer an adequate supply of this shellfish to satisfy world demand. The price of edible abalone meat has escalated fivefold over the last ten years.
The normal life cycle of an abalone starts with a spawning process involving the dissemination of eggs by the ripe female and a fertilization thereof in the aqueous environment by male sperm. Spawning has been successfully induced in commercial mariculture operations in Japan and in experimental programs in the United States.
The fertilized abalone eggs, which are about 150 microns in diameter, undergo several stages of development in the first 36 hours, and then hatch to become free-swimming larvae. These larvae hatch initially without a protective shell, but within approximately six hours an initial shell is developed. The ability of the larvae to swim is provided by a velum, which includes hundreds of hairlike cilia that are rapidly moved by the animal to propel it through the water. During this larval stage, it is believed that the primary source of nutrition is obtained from the egg yolk still contained within the body of the larva. After approximately four days under controlled conditions, and this time period may vary somewhat in nature, the larvae develop a foot which allows them to settle and then metamorphose from a swimming form into a crawling snail-like animal. The larvae, which are about 150 microns in greatest dimension at the time of hatching, grow to approximately 250 micron size in the four-day period.
When the swimming larvae reach the last stage of development, which, as noted above, occurs in approximately four days, they begin to search for suitable substrate upon which to settle, and metamorphose from a swimming animal to a surface crawling animal. This process of metamorphosis is a very interesting and complicated one, and is described in greater detail in our copending application Ser. No. 955,944, filed Oct. 30, 1978, and entitled Abalone Mariculture.
The fertilized abalone eggs and the larvae hatching therefrom are extremely delicate. In their native environment, a substantial percentage of the eggs do not hatch and a goodly percentage of the hatched larvae do not live through the first four days. With controlled fertilization of good quality eggs, we have been able to achieve a hatchability percentage as high as 90%. Moreover, in artificial culture, if this percentage is significantly below 90%, it is a likely possibility that the resultant larvae are not healthy and will not develop normally. Further, we have been able to obtain a survival rate of such larvae of about 90% through the first four days of their life.